1. Field of the Invention
The present invention relates to a tracing control method, and more particularly, to a tracing control method by which an overshot machining of a cutter into a workpiece at a region of a model where the shape thereof undergoes an abrupt change is prevented, whereby the overall tracing time can be shortened.
2. Description of the Related Art
In a tracing control, the amounts of displacement of respective axes applied to a stylus are detected by a tracer head, speed commands of the respective axes are calculated in a tracing calculating circuit by using these amounts of displacement, motors of the respective axes are driven in accordance therewith, and the tracer head is moved along the surface of a model while the cutter is moved relatively against a workpiece at the same speed, and by repeating this motion the workpiece is machined to the same shape as the model.
Nevertheless, such a tracing control has a problem in that an overshot machining might occur at regions of the model where the shape is abruptly changed if the tracing speed is too high.
To solve this problem, the applicants filed Japanese Patent Application No. 1-192383 wherein the title of the invention is "TRACING CONTROL METHOD", on Jul. 25, 1990. In this Patent Application No. 1-192383, a region in which an abrupt change of the model surface occurs is detected based on the amounts of displacement of the respective axes obtained by the tracer head, the position in the tracing direction is stored, and the tracing speed is lowered only in a section within the range of predetermined distances in front of and behind the position in the tracing direction stored this time, in the next tracing pass, to prevent an overshot machining and accordingly, to shorten the overall tracing time.
Nevertheless, because the position of an actual abrupt change region in the next tracing pass is not always at the same position as that of the abrupt change region detected in this tracing pass, the range of the deceleration section can not be set to a value small enough to cope with this anomaly, and thus the desired shortening of the tracing time cannot be attained.